// Production steps of ECMA-262, Edition 5, 15.4.4.18
// Reference: http://es5.github.io/#x15.4.4.18
if (!Array.prototype.forEach) {
  Array.prototype.forEach = function(callback, thisArg) {
    var T, k;

    if (this == null) {
      throw new TypeError(" this is null or not defined");
    }

    // 1. Let O be the result of calling toObject() passing the
    // |this| value as the argument.
    var O = Object(this);

    // 2. Let lenValue be the result of calling the Get() internal
    // method of O with the argument "length".
    // 3. Let len be toUint32(lenValue).
    var len = O.length >>> 0;

    // 4. If isCallable(callback) is false, throw a TypeError exception.
    // See: http://es5.github.com/#x9.11
    if (typeof callback !== "function") {
      throw new TypeError(callback + " is not a function");
    }

    // 5. If thisArg was supplied, let T be thisArg; else let
    // T be undefined.
    if (arguments.length > 1) {
      T = thisArg;
    }

    // 6. Let k be 0
    k = 0;

    // 7. Repeat, while k < len
    while (k < len) {
      var kValue;

      // a. Let Pk be ToString(k).
      //    This is implicit for LHS operands of the in operator
      // b. Let kPresent be the result of calling the HasProperty
      //    internal method of O with argument Pk.
      //    This step can be combined with c
      // c. If kPresent is true, then
      if (k in O) {
        // i. Let kValue be the result of calling the Get internal
        // method of O with argument Pk.
        kValue = O[k];

        // ii. Call the Call internal method of callback with T as
        // the this value and argument list containing kValue, k, and O.
        callback.call(T, kValue, k, O);
      }
      // d. Increase k by 1.
      k++;
    }
    // 8. return undefined
  };
}

Array.prototype.myforEach = function(callback, thisArg) {
  const O = this;
  let k = 0;
  let T, len;

  if (this == null) {
    throw new TypeError(" this is null or not defined");
  }

  len = O.length;

  if (typeof callback !== "function") {
    throw new TypeError(callback + " is not a function");
  }

  if (arguments.length > 1) {
    T = thisArg;
  }

  while (k < len) {
    var kValue;
    // 已删除或者未初始化的项将被跳过
    if (k in O) {
      kValue = O[k];
      callback.call(T, kValue, k, O);
    }
    k++;
  }
};

const arraySparse = [1, 3, , 7];
let numCallbackRuns = 0;

arraySparse.myforEach(function(element) {
  console.log(element);
  numCallbackRuns++;
});

if (!Array.prototype.some) {
  Array.prototype.some = function(fun/*, thisArg*/) {
    'use strict';

    if (this == null) {
      throw new TypeError('Array.prototype.some called on null or undefined');
    }

    if (typeof fun !== 'function') {
      throw new TypeError();
    }

    var t = Object(this);
    var len = t.length >>> 0;

    var thisArg = arguments.length >= 2 ? arguments[1] : void 0;
    for (var i = 0; i < len; i++) {
      if (i in t && fun.call(thisArg, t[i], i, t)) {
        return true;
      }
    }

    return false;
  };
}

if (!Array.prototype.every) {
  Array.prototype.every = function(callbackfn, thisArg) {
    'use strict';
    var T, k;

    if (this == null) {
      throw new TypeError('this is null or not defined');
    }

    var O = Object(this);

    var len = O.length >>> 0;

    if (typeof callbackfn !== 'function') {
      throw new TypeError();
    }

    if (arguments.length > 1) {
      T = thisArg;
    }

    k = 0;

    while (k < len) {

      var kValue;
      if (k in O) {
        kValue = O[k];
        var testResult = callbackfn.call(T, kValue, k, O);

        if (!testResult) {
          return false;
        }
      }
      k++;
    }
    return true;
  };
}